The present invention relates to light fixtures and particularly to light fixtures having multiple different wavelengths of LEDs.
Luminaires or light fixtures are capable of reproducing a wide gamut of colors by combining light from, for example, a plurality of LED light sources. White is a color that is commonly desired to be produced by a luminaire. To produce white, it is common to energize all LEDs in the luminaire so that white light with the highest luminous flux is produced.
When creating white light from LEDs, it is often characterized by the Correlated Color Temperature (CCT) from warm white (around 2500K) to cool white (around 5000K). In general, warm white is produced using less blue light and more red light, and cool white is produced using more blue light and less red light.
In addition to color temperature, light can be characterized by its ability to accurately render color on a subject. The Color Rendering Index (CRI) provides a representation of an artificial light's accuracy of producing the full range of colors in a subject in comparison to a standardized source (typically a source representing an incandescent lamp or daylight). A perfect CRI score is 100, which indicates that the artificial light source renders color to the human eye as well as the standardized source.
A newer method to evaluate color rendition is TM-30 (Rf), which includes a system for evaluating the fidelity of a light source when compared to a reference tungsten halogen source or to daylight. TM-30 (Rf) is determined using a well-defined process, such as is described in IES TM-30-15 published by the Illuminating Engineering Society (IES). In particular the (Rf) metric defined in TM-30 is a measure of rendering color fidelity.
In a setting in which cameras (e.g., still cameras or video cameras) are being used, light selection must take into account the fact that cameras do not see light the same way as the human eye. This is particularly true for digital cameras that utilize CCD or CMOS sensors as the imaging-capturing interface. Due to this difference in the human eye observer and the digital camera, subjects, such as human skin tones, when illuminated by a light with a high CRI or TM-30 (Rf) (which looks good to a human observer) can appear quite poor to a digital camera.
In order to predict a light's ability to accurately render color when captured by a television camera and viewed on a display, the Television Light Consistency Index (TLCI) was created by the European Broadcasting Union (EBU). The TLCI is based on a mathematical calculation implemented in software called TLCI-2012, which is specified in EBU Tech 3355. Like the CRI, the TLCI indexes light up to a maximum score of 100. In general, when recording on a camera in a studio setting, a higher TLCI is considered desirable.